Telephone system



H. W. ULRICH.

TELEPHONE SYSTEM.

APPLICATION FILED JULY 11,1919.

1,408,046; Patented Feb. 28, 1922.

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TELEPHONE SYSTEM. APPLICATION FILED JULY 11.1919.

Patented Feb. 28, 1922.

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H. w. ULRICH.

TELEPHONE SYSTEM.

APPLICATION FILED JULY 11,19l9.

1,408,046. Patented Feb. 28, 1922.

3 SHEETS-SHEET 3'- Tali: JEFM /nven/0/ UNITED STATES PATENT OFFICE.

HORACE W. ULRICH, 03 EAST ORANGE, NEW' JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Application filed July 11,

To all whom it may concern:

Be it known that I, Henson \V.,UL1:IGH, a citizen of United States, residing at East Orangqin the county oi. Essex, State of New Jersey, have invented certain new and useful Improvements in Telephone Systems, of which the following is a fiillll, clear, concise, and exact description.

This invention. relates to telephone systems, and more particularly to such systems employing long telephone transmission lines equipped with anmliliers or repeaters.

The primary object oif this invention is the provision oi? a telephone system embracing telephone transmission lines equipped with am 'iliiiers for amplifying; either talking or signaling currents or both, the transll'llSSlOil eflicicncy or equivalent o't which will be maintained substantially constant regardless 0t variations in conditions affecting the electrical characteristics of the transmission lines.

It .is well known that the transmission equivalent or cllicieuey of a telephone trans mission line varies due to many different causes. Chief among the many causes contributing to variations in the transmission efficiency of a telephone transmission line may be mentioned variations in resistance, capacity and inductance of the line and as sociated apparatus due to variations in voltages and temperature.

The present invention contemplates the elimination of the diiiic ilties hereto'tore encountered due to such variations by compensating therefor by varying some adjustable element or elements of the transmis sion line.

In attaining the objects of the present in yention, there is associated with a transmis sion line teri'ninating at widely separated stations control apparatus conditioned for operation upon the actuation of a switching derice at one end oi the transmission line and operating upon the restoration of the switching: device to normal condition. The operation of the control apparatus discon nects the transmission line from the terminating apparatus. forms a loop circuit thereof, connects a responsive device with the loop circuit for thereafter controlling the control apparatus. and simultaneously sets the amplifiers associated. with the transmis- Specification of Letters latent.

Patented Feb. 28, 1922.

1919. Serial No. 310,042.

sion line so that the amplification thereof is greater than the attenuation of the loop circuit thereby causing the circulation of power in the loop circuit. The responsive device is operated by the power circulating in the loop circuit, and causes the control apparatus to gradually decrease the amplification of the amplifiers until the circulation or power ceases, whereupon the responsive appa "atus ceases to respond. restoring the control appartus to normal condition.

For a more complete understanding of the present invention, reference should be had to the following description considered in connection with the accompanying drawings, which with Figs. 1., 2 and 3 thereof when placed end to end with Fig. 1 at the left, illustrate one embodiment thereof. For e mvenience, like apparatus at the two terininating stations will be designated by the same reference clmracters, that at one station being without and that at the other station with primes.

There is shown in the drawings a tourwire repeater circuit of the type disclosed in the Van Kesteren lt atent, No. 1,189,411, July l, 1916., which terminates at and interconnects two widely separated ofiices or stations A and (l. This four-wire circuit, Which comprises a pair of transmission lines E and V1 for transmitting in opposite direction, extends through an intermediate station B at which are located amplifiers or repeaters RE and RVV connected in the re spective lines E and W of the four-wire circuit. The amplification or gain of the amplifiers RE and RW is controlled by adjustable potentiometers PE and PlV associated with the input circuits of the respectire amplifii-u's. T he adjustment of these pocntiometers is controlled by an automatic switch controlled from the oflices A and over a simplex circuit built partly upon the transmission line E and partly upon the ansmission line W. This automatic switch comprises roiiatable contact arms (I, Z), c and (ii mounted upon a common shaft the stepby-step r nee of which is controlled by a seli -intcrropting; motor magnet MM. Each 01": the contact arms when rotated successi'vely engages stationary contacts, those associated with the contact arms a and 7) (-0-- operating;- herewith to control the adjustment of the potentiometers PE and P'W, those associated with contact arm 0 controlling the circuit of the motor magnet MM and those associated with contact arm (Z controlling signallamps 7 6 and 77 and a buzzer 79. At the offices A and C, the four-wire transmission circuit is terminated through.

two-wire terminating circuits T and T respectiyely, thetransmission lines E and W of the four-wire transmission circuit being associated with the terminating circuits T and T throughthe windings of the repeat ing coils 5 and 5 and the auto transtorm- 'ers, 6 and 6. 'At the o'flice A there is pro vided a cord circuit D for establishing con nections with the two-wire terminating circuit T of they four-wire circuit and a similar cordcircuit' D located atthe oflice G for establishing connections with the two-Wire terminating circuit T of the four-wire circuit thereat. The apparatus shown in Fig. 1 is shown at the oflice A, that in Fig. 2 at the oflice. B and. that in Fig. 3 at the oliice C.

The opeiator at the oliice A, desiring to establish connection with the oflice C by way of the four-wire transmission circuit,

inserts plug 10 v of cord circuit D into jack.

of output coil 64, winding of relay 17, lefthand normal contact of relay72, then in parallelthrough the secondary windings of output coil ist, the two line-wires of transmission/line and theline windingsot repeating coil 15C, windings ofrelays 16 and l5 an. dfcontact or relay l l to grounded 1 negative battery; Upon the release of relay 15, relaylS operates over a circuit from batterythrough resistance ll), winding and left-hand normal contact of relay 1S and the back contact of relay 15 to ground. Relay l8in'operatinp; opens its normalcontacts and 'closesjits alternate contacts establishing a loclringcircuit for itself through its lefthand alternate contact to ground. Upon th'e closure of the rlght-hand alternate contact of relay18 an energizing circuit for relay 20 is prepared. The release of relay 17 causes theenergization of the slow re lease relay 21 which, in closing its left-hand contact, clo'ses the filament circuit of the amplifiers RE and RVV and an amplifier 25'. .Withthe output circuit or' amplifier 25 is associated a relay 26. The release of relay 15 causes the energization and. locking-up ct relay 18 which prepares an energizing circuit for relay 20.

In order to signal the office C the oper s;

ator the office A may now actuate ringing key 27, thereby causing the energiz ation-of ringing response relay 28 over a circuit from a source of 16 cycle ringing current 29 through the lower alternate contact of the ringing key 27, ring contacts of the plug 10 and tie ]a-('l 11, lower normal contact of ringing relay 30, lower winding of relay,

28, condenser 31, upper winding of relay. 28, upper normal contact of ringing relay 30, tip contacts of the jack 11 and theplug 10 and the upper alternate contact of ringing key 27 to ground. Relay 28 in operating causes the deener' 'ization of a normallyen-v ergized rela 32. Relay32 in releasing its armature causes the operation of relays] 33 and 34 over a circuit from battery through the windings ofthese two relays inseries and the contact of relay 32, to ground. Re-

lay 33 in operating disconnectsthe transmis-- sion line W from the terminating circuit T.

The operation of relay 34 causes the energization oi ringing relay 35 which connects.

a source of 133-5 cycle ringing current with the transmission line E which traverses the.

primary winding of input coil 40. Through the inductive action of the inputcoll 4L0. signaiing current is admitted. to the input C111 cuit or the amplifier RE, amplified thereby into the output circuit or" the amplifier and causes the operation of ringing response relay l1 connected in the output circuit.

Ringing response relay 41 in opening its right hand contact causes the release of a nor- This,

inally energized slow release relay 4L2. relay in opening its normal contact opens a contact in the shunt of the potentiometer PE and in closing its left-hand contact connects a condenser 43 in parallel with the primary winding of the input coil 40. The

capacit of this condenser 48 is such asto.

form with the primary winding of the input coil 40 when connected in parallel therewith, loop circuit tuned to the frequency of the slgnaling current. to transmit most efi iciently to the. amplifier RE the frequencies of the signaling current. The itHlPllllQCl signaling current in theoutput circuit of the amplifier RE traverses the primary windings of the output coil 44 and is repeated thereby into the line E extending to the station C and is repated thereat through the windings or simple); coil as and r the windings of the auto-transformer 6', causing the energizatien Oi ringing response relay 4:6, The energization of ringing response relay 46 causes the deenergization of a normally energized relay t7. Upon the closure of the Contact of-this relay 47, relays 33 and a9 operate. in series. The former (relay 33) disconnects line E from the This tuned circuit serves terminating circuit T and the latter (relay 49) causes the energization of ringing relay 30'. The operation of this ringing relay 30causes the operation of ring-up relay 51 over a circuit from a source of 16 cycle ring- 54L is in parallel with the locking winding of relay 51 and is lighted upon the closure of this locking circuit. The lighting of this lamp 54 serves as a line signal to the operator at the oflice C.

Upon the restoration of the ringing key 27 to normal position, ringing response relay 28 releases its armature causing the energization of relay 32, whereupon relays 33, 34 and 35 release. Upon the release of ring ing relay 35, ringing response relay ll is deenergizecl causing the energization of relay 42, which restores the input circuit of the amplifier RE to normal condition. Also upon the release of ringing relay 35 ringing response relay 46 is also deenergized. Re lay4t7 thereupon operates causing the re lease of relays 33, 49' and 30.

The operator at the oilice C upon observing the light-ed condition of the lamp 54- may insert plug 10 of the cord circuit D into the jack 11, thereby operating relays 12' and 13'. Relay 14 operates upon the energization of relay 13' and introduces an other break in the simplex circuit including the relays 15, 16, 17, 16 and 15. The opening of the normal contact of relay 13 causes the release of relay 51 and the extinguishment of the lamp 54-. The operators may actuate the listening keys 55 and necting the respective telephone sets in circuit, and may then converse It is to be understood, of course, that the cord circuits l) and D provided at the offices A and C may and usually do form connecting links between the four-wire circuit and telephone lines terminating at the respective oiiices A and C. These lines, however, and'the remaining portion of the cord circuits D and D form no part of the present invention and are'there'fore not shown in the drawings.

At the conclusion of the conversation between the operators or between the subscril ers at the stations on the lines joined through the cord circuits and the tour-wire repeater circuit, the operator at the office C may gire a disconnect signal to the operator at the ofiice A and thereupon disconnect. the cord circuit D from the two-wire terminating circuit T of the four-wire circuit In i ing the disconnect signal the operator at the oflice C actuates ringing key 27 connecting a source of 16 cycle ringing current 29 in circuit to cause the -n1ergization of ringing response relay 28. Rel 32- thereupon releases causing the energization of relays 33' and er. The former disconnects the transmission line it) from the terminating circuit T and. the latter causes the energization of ringing relay 35 which connects a source of cycle ringing current with transmission line causing the energization of ringing response relay 61 at the station 13 and ring ll response relay 4:6 the station A. The e gizaticn oi? ringing response relay 61. causes the deenergization of a normally nergized slow release relay 62 which opens "he shunt if the potentiometer Pl V -from cross the input circuit or" the amplifier RlV nd connects a resonating condenser 63 in arallcl relation with the primary Winding t the input coil 60. The energization of :ingi response relay 46 causes the release 47, whereupon relays 33 and 49 V ing relay 304 Re Zing connects a source of 16 g :1 rent 52 in circuit with the a winning or"- ring-up relay lay 56 thereupon locks up over a cir-- cattery throu h the contact of righthand w iding of relay 56 and cents thereof: to ground. Supervisory lamp 5'? also lights upon the cnergiaation of relay 56 and serves as a disconnect signal on. The release cl ring; n

re sponse relay causes the energiaation of 4:7 whereupon relays stand 30 re- A restoring the apparatus of. the terminan .ig circuit to normal position.

. ion of the cord circuit D from the terrn'nating circuit T" by the removal of the plug 10 from the jack 11 causes the release oi relays l2 and i3. The

causes the deenergiaause relay 1 2;. This relay and its conniai on relay 1 at the oilice are made slow in releasing: to prevent operation of the relays in the simplex clue to any momentary energization o sleeve relays.

the oitice A observing the CQHHulOIl of the supcryisory lamp release re a 13? tion o1 slow rel "1% mal contact of relay 15 to ground.

lay 12in releasing. opensthe locking .circuit of relay 56, whereupon the lamp 557 is extinguished. .The release of relay 13 causes the deenergization of slow release relay 14.

Relays 1 1 and 1 1 are bothdeenergized at this time so that the simplex circuit is re established causing the relays 15, 16, 17, 16 and 15, connectedtherein, to be energized. Upon the energization of relays 15 and 16, relay 20 operates over a circuit from battery through the winding of relay 20, normal contact thereof, right-hand alternate contact of relay 18, contact of relays 16 and the nor- Relay 20 in operating completes a locking circuit for itself from battery through its Winding and inner :righthand alternate contact and the contact of relay 39 to ground. Relay 20 in operating also causes the operation-of disconnectingrelays 36 and 37 which disconnect the lines E and W from: the windings of the :repeating coil 5 and the auto-transformer 6 and connects these two lines together through a pair of looping conductors 38. i The lower movable contact of relay 37 is in parallel with the'normal contact of relay 14:, so that the energization of relay 14 by the insertion of the plug 10 in the jack 11 will not disturb the simplex circuit while relays 36 and 37 are energized. 1 While these operations are taking place at the oiiice A, similar operations are going on at the office C; That is, the energization of relays 15 and 16 causes relay 20 to energize and lock up over circuits similar to those traced in connection with. relay 20. Relay 2O in operating causes the operation of disconnecting relays 36 and 37 which disconnect the lines E and W from the windings of the auto-transformer 6' and the repeating coil 5 and con nects these lines together by means of a pair of looping conductors 38'.

Simultaneously with the above described operations taking place at the stations A- the right-hand contact of slow release relay 21 is opened so that start relay is energized over a circuit from battery through the winding of start relay 70, contact of slow release relay 71, right-hand contact of slow release relay 21 and thenormal contact of relay 17 to ground. Relay 21 when fully released opens the filament circuit of the amplifiers and also opens the energizing circuit of start relay 70. Before this energizing circuit is opened, however, a locking circuit for start relay 70 is completed from battery through the winding of relay 70, left-hand contact thereof, right-hand normal contact of relay 72 and the winding of relay 73 to ground. Relay 73 operates over this circuit bridging the input circuit of theamplifier 25 across the transmissionline E and closing'a circuit throughthe polarizingwindings of singing response relay 26. This cir j cuit may be traced from battery through re-' sistance 74, outer right-hand and lefthandwindings of singing response relay 26and the left hand contact of relay 73 to ground. Upon the operation of relay-70, as previously described, a circuit is completedthrough the motor magnet MM whicht-hereuponadvances the contact arms a, b, c and d until the contact arm -0 engages the first contact connected with the terminal of the winding of relay 72, whereupon this relay immedlately operates- Relay 72 in operat- Big 013G118 its left-hand contact,-which is in the simplex circuit, thereby causing the -release of relays 15, 16, 17, 16-an,d 15 ineluded illlllllS simplex circuit. The closure of thealternate contact of relay-72 causes the energization of slow release relay 71 over a circuit from battery through the winding of relay 71, alternate contact of relay 72 and thewinding of relay 73'to ground. Relay 72 in opening its right-hand normal contact 7 opens the locking circuit'of start relay 70, while slow releaserelay 71 upon energizing opens the originalenergizing circuit of the start relay 70. Start relay 70 therefore releasesopening the operating circuit of the motor magnet MM. The motor magnet MM therefore ceases toadvance the contact arms a, b, c, and d oi theautomatic switch. The release of relay"17 upon the opening of the simplex circuit at the left-handcontact of relay 7 2, causes the energization of theslow release relay 21 which at its left-hand contact closes the'filament CTlI'CUlt'Of the amplifiers RE, RVVand 25. The deenergization 20 and the alternate contact of relay 15"to Relay 18 thereupon releases its ar- 1 ground.

matures preparing at its right-hand normal contact an energizing circuit for relay 39.

In a similar manner the release of relay 15 establishes a short circuit for the'winding of relay 18 causing the release thereof. Relay 18 then in closing its left-hand normal contact prepares an energizing circuit for relay- 39.

When the contact arm 0 engages the first contact connected with the'windin'g of relay 72, the contact arms a and 7) are connected to the extreme left and right-hand effective contacts of the respective potentiometers and PW. With this setting of the potentiometers, amplifiers RE and RVV produce the highest degree of amplification which 18 greater than the attenuation of the loop cir cuit. A circulation of power over the loop circuit therefore results The input circuit of the amplifier 25 is connected in bridge of this trunk so that the relay 26 connected in the output circuit of the amplifier 25, is operated by the power circulating in the loop circuit and opens its contact thereby opening the circuit of relay 81 which releases. The closure of the left-hand contact of this relay 81 connects a constantly driven interrupter 82 in circuit with the winding or: the motor magnet MM, whereupon this motor magnet MM becomes effective to advance the contact arms a, Z), c and (Z step-by-step in the direction of the arrows. The closure of the right hand contact of relay 81 establishes a holding circuit for relay 72 so that this relay does not release upon the movement of the contact arm 0 out. of engagement with the contacts connected with the terminal of the winding of relay 72. The contact arms a, b, c and o are advanced step-by-step, the contact arms a and b gradually adjusting the potentiometers PE and PW thereby gradually reducing the amplification of the amplifiers RE and 'R- until the circulation of power ceases.

As the circulation of power ceases, relay 26 ceases to respond and closes its contact causing the energization of relay 81 which then opens the operating circuit of the motor magnet MM which ceases to advance the contact arms. The opening of the energizing circuit of relay 72 at the right-hand contact of relay 81 causes the deenergization of relay 72 which opens its alternate and closes its normal contacts. Upon the closure of the left-hand contact of relay 72, the simplex circuit is reestablished causing the reenergization of relays 15, 16, 17, 16 and Relay 71 is slow in releasing so that upon the opening of its energizing winding; at the alternate contact of relay 7 2 the contact of relay 71 is not closed until after the opening of the contacts of slow release relay 21 whose energizing circuit is opened by the energization of relay 17 in the simplex circuit. In this manner the energizing circuit of start relay is not reestablished upon the deenergization of relay 72. The deenergization of relay 72 also causes the deenergization oi; relay 73 which opens the polarizing circuit of relay 26 and disconnects the associated amplifier 25 and the relay 26 from the loop circuit formed by the transmission lines E and W.

The energization of relays 15 and 16 in the simplex circuit causes the operation of relay 39 over a circuit from battery through the winding of relay 39, outer right-hand alternate contact of relay 20, right-hand normal contact of relay 18 and the normal contacts of relays 16 and 15 to ground. Belay 39 in operating opens the locking circuit of relay 20 which releases causing the deenergization of disconnect relays 86 and 37 and the deenergization of relay 35. whereupon all apparatus at the station A is restored to its normal condition. In a similar manner the energization of relays 15 and 16 in the simplex circuit at the station C causes the operation of relay 39 which opens the locking circuit of relay 2-0. Relay 20' in releasing causes the deenergization of disconnect relays 36 and 37 and the release of relay 35. All apparatus at the station 0 is therefore restored to its normal condition.

In adjusting the potentiometers PE and PlV to gradually reduce the amplification of the associated amplifiers RE and RV until the circulation of power in the loop circuit ceases, the contact arms may be stooped in such position that the contact arm (Z engages one of the extreme right-hand or extreme left-hand contacts connected to the respective signal lamps 76 and 77, should the con tact arms be stopped in such a position one or the other of the lamps would be lighted and the relay 78 operated. The buzzer 79 would also operate. The lighting of one or the other of the lamps and the operation of the buzzer would serve as a signal to the attendant at the station E, indicating an ab normal adjustment of the potentiometers. This would indicate that there is some condition in one or the other of the transmission lines E or requiring attention on the part of the attendant. The lamp 76 is liahted and the buzzer 79 operated ea h time the potentiometers are set for the highest decree of 23.111 of the amplifiers RE and RW. The length of time the lamp is li hted and the buzzer is operated is very short and merely indicates that the potentiometers are being: adjusted. It is the continued licht nq of one of the lamps and the operation of the buzzers which indicate an abnormal setting of the potentiometers.

The actuation of either of the keys 58 and 58 provided at the respective stations A and C and the restoration of the actuated key to normal conditions causes the control apparatus to loop the transmission lines torrether. to connect therewith the relay 26 and to ad just the potentiometers in the some manner as when. a connection is built up over the four wire circuit and then broken down as described above.

What is claimed is:

1. In a telephone circuit, in combination, a four-wire transmission circuit including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines. an automatic switch, means under control of the automatic switch for determining the amplification of the amplifiers, means for interconnecting the ends of the transmission lines to form a loop circuit thereof and for simultaneously advancing the switch to a predetermined position thereby setting the amplifiers for the highest degree of amplification so that power circulates over the loop circuit, power 5 for responsive means for advancing the switch until the circulation of power ceases, and means responsive to interruption of the circuit for connecting said power responsive 5 means with said loop circuit.

2. In a telephone circuit, in combination, a four-wire transmission circuit including a pair oftransmission lines for transmitting in opposite directions, amplifiers for the transmission lines, an automatic switch, meansunder control of the automatic switch for determining the amplification. of the V amplifiers, means for interconnecting the ends of the transmission lines to "form a loop circuit thereof and for simultaneously advancing the switch to a predetermined position thereby setting the amplifiers for a de gree of amplification greater than the atftenuation ofthe transmission lines so that 0 power circulates over the loop circuit, power responsive means for advancing theswitch to reducethe amplification of the amplifiers until the circulation of power ceases, and ,means responsive to interruption of the circuit for connecting said power responsive means with said loop circuit.

3. In a telephonesystem, in combination, a four-wire transmission circuit including a pair of transmission lines, for transmitting in opposite directions, amplifiers for the transmission lines, an automatic switch, ,means under control of the automatic switch ,for determining the amplification of the ,amplifiers, means for interconnecting the ends of the transmissionlines to form a loop circuit thereof and for advancing the switch to a predetermined position thereby setting vthe amplifiers for the highest degree of amplificationso that power circulates over 40 the loop circuit, and means controlled by '50 transmission line s, an automatic switch,

means under control of the automatic switch to e ining the amplification of the am- Qtrolled over-"a circuit in lngpo ons otboth transmission lines terconnecting the ends of the transmissionlines'to liorm a loop circuit thereof and ,for advancing. the switch to a predetermined position thereby setting the amplifiers for i theihighest degree of amplification so that '60 7 power circulates: over the loop circuit, power responsive m ean's for advancing the switch li ntil the circulation of power ceases, and means responsive to interruption of the cirhit for connecting said power responsive means with said loop circuit.

1 ,aoaoae 5. In a telephone system, in combination, a tour-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines located at an intermediate station, means for interconnecting the ends of the transmission lines to form a loop circuit thereof, means at the intermediate station controlled from a terminal station for increasing the amplification of the amplifiers so that power circulates over the loop circuit, power response means at the intermediate station, means thereat controlled from a terminal station-for connect ing the powen' response means with the loop circuit, and means controlled by the power response means for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

6. In a telephone system, in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for thetransmission lines located at an intermediate station, means for interconnecting the ends of the transmission lines to form a loop circuit thereof, means at the intermediate station for increasing the amplification of the amplifiers so that power circulates over' the loop circuit, power responsemeans at the intermediate station, means 'thereat controlled from a terminal station for connecting the power response means with the loop circuit, and means controlled the power response means for gradually decreasing the amplification of the amplifiers until the circulation of power ceases] 7. In a telephone system, in combination, a 'iour-wire transmissioncircuit interconnecting two terminal stations, and including a pair oiv transmission lines for transmitting in opposite directions, amplifiers tor the transmission lines located at an intermedi ate station, means controlled over a circuit including portions of both transmission lines for interconnecting the ends of; the

transmission lines to form a loop t rcui't thercofl means at the intermediatestation for more sing the amplification ofthe-amplifiers sothat power circulates over; he loop ting in opposite directions, amplifiers for the transmission lines located at an intermediate station, power response means at the intermediate station, means controlled over a circuit including a portion of both trans mission lines for interconnecting the ends of the transmission lines to form a loop circuit thereof and for simultaneoiisly connecting thereto the power response means, means at the intermediate station for increasing the amplification of the amplifiers so that power circulates over the loop circuit, and means therefor controlled by the power re sponse means for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

9. In a telephonesystem, in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for trans mitting in opposite directions, amplifiers for the transmission lines located at an intermediate station, means for interconnecting the ends of the transmission lines to form a loop circuit thereof, means at the intermediate station and controlled from a terminal sta tion over a circuit including portion of both transmission lines for increasing the amplification of the amplifiers so that power circulates over the loop circuit, and means at the intermediate station responsive to such circulating power for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

10. In a telephone system, in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transn'iitting in opposite directions, each transmission line comprising two line wires, amplifiers forthe transmission lines located at an intermediate station, means for interconnecting the ends of the transmission lines to form, a loop circuit thereof, means at the intermediate station and controlled from a terminal station over acircuitincluding portion of the two line wires of one transmission line connected in parallel and a portion of the two-line wires of the other transmission line connected in'parallel for increasing the amplification of the amplifiers so that power circulates over the loop circuit, and means at the intermediate station responsive to such circulating power for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

11. In a telephone system in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines located at an intermediate station, relays at each terminal station for interconnecting the ends of the transmission lines to form a loop circuit. thereof, means at the intermediate station. controlled from a tern'linal station over a circuit including portions of the two transmission lines for increasing the amplification of the amplifiers so that power circulates over the loop circuit, means in the circuit including portions of the two transmit. fii'on lines for sin'iult-aneously rendering the interconnecting relays operative and "the amplification increasing means effective, and means at the intermediate station responsive to the power circulating over the loop circuit for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

12. In a telephone system, in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting; in opposite directions, amplifiers for the transmission lines located at an intermediate station, relays at the terminal stations for interconnecting the ends of the transmis sion lines to form a loop circuit thereof, a control relay at each terminal station adapted when energized to cause the operation of the connecting relays thereat, means at the intermediate station controlled from a terminal station for increasing the amplification of the amplifiers so that power circulates over the loop circuit, means at the intermediate station responsive to such circulating power for gradually decreasing the amplification of the amplifiers until the circulation of power ceases, and means in the circuit including portions of the two transmission lines for causing the deenergizatiou of the control. relays at the terminal stations.

18. In a telephone system, in combination, a four-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines located at an intermediate station, relays at the terminal stations for interconnecting the ends of the transmission lines to form a loop circuit thereof, operating ci cuits for the interconnecting relays, a switch, primary control relays at each terminal station responsive to the actuation of the switch, a secondary control relay at each terminal station responsive to the restoration of the switch to normal position for closing the operating; circuits of the interconnecting relays, means controlled by the operation of the switch and the restoration thereof to normal position for increasing, the amplification of the amplifiers so that power circulates over the loop circuit, and means responsive to such circulating power for gradually decreasing the amplification of the amplifiers until the circulation of power ceases.

14. In a telephone system, in combination, a four-wire transmission circuit intercom necting two terminal stations and including a :pair of transmission lines for transmitting in opposite directions, amphfiers tor the transmission lines, connecting relays at the terminal stations tor interconnecting the switch is restored to normal condition for closing the operating circuits of the connecting relays, means for increasing the amplification of the amplifiers so that power circulates over the loop circuit, and means responsive to such circulating power for gradually decreasing the amplification or the amplifiers until the circulation of power ceases.

15. In a telephone system, in combination, a four-wire transmission circuit interconne'ctingtwo terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines connecting relays at the terminal stations for interconnecting the ends of the transmission lines to form a loop circuit thereof, a switch, a primary control relay at each station energized upon the actuation of the switch, a secondary control relay at each station energized upon the restoration of the switch to, normal condition for controlling the connecting relays, means for increasing the amplification of the amplifiers so that power circulates over the loop circuit, means at each station and controlled by the amplification increasing means for causing the deenergization of the primary control relays, means for gradually decreasing the amplification of the amplifiers until the circulation of power ceases, and means thereafter controlled by the amplification decreasing means for causing the deenergization of the secondary control relays.

16. In a telephone system, in combination, a tour-wire transmission circuit interconnecting two terminal stations and including a pair of transmission lines for transmitting in opposite directions, amplifiers for the transmission lines, connecting relays at each station for interconnecting the ends of the transmission lines to form a loop circuit thereof, operating circuits for the connecting relays, a switch, a primary control relay at each station energized upon the actuation of the switch, a secondary control relay at each station energized upon the restoration oi"? the switch to normal condition for completing the operating circuits, means for increasing the amplification ofthe amplifiers so that power circulates over the loop circuit, means-responsive to such circulating power for gradually decreasing the amplification of the amplifiers until the cir culation of power ceases, andmeans controlled over a circuit including a portion of one of the transmission lines and a contact of one of the connecting relays for causing the deenergization of the primary and secondary control relays.

In witness whereof, I hereunto subscribe my name this 8th day of July, A. 1)., 1919.

HORACE W, ULRICH. 

